The invention relates generally to methods for controlling the operation of gas turbine engines and, more particularly, to a method of detecting flame-holding or flashback conditions in gas turbines using combustion dynamics.
Gas turbines engines include a compressor, a combustor, and a turbine coupled to the compressor. The combustor can include a plurality of combustor cans. Compressed air and fuel are delivered to the combustor cans to produce high-velocity and high-pressure combustion gases. These combustion gases are discharged to the turbine. The turbine extracts energy from the combustion gases for producing power that can be used in several ways such as, for example, to power the compressor, to power an electrical generator, or to power an aircraft.
Gas turbine engines operate under different load conditions that necessitate varying combustion operating conditions for the combustors to meet desired performance. A gas turbine combustor is designed to stabilize a flame at a desired location to ensure uninterrupted operation. However, under certain conditions during combustion of fuel, combustors can experience flame holding or flashback. Flashback is a phenomenon in which a flame travels upstream of the designed stabilization location towards fuel and air injection locations. During flame holding, the flame stabilizes upstream without traveling from a downstream location. In the following discussion, the term “flashback” is used to represent both flashback and flame holding, since the discussion applies equally to the both flashback and flame holding.
The conditions for occurrence of flashback change under different operating conditions of temperature, pressure, fuel to air ratio, and on type and composition of fuel. Flashback can occur through two different physical mechanisms broadly categorized as premixed and diffusion flashback. The geometry of a nozzle and its components play an important role in making a particular nozzle either flashback tolerant or flashback resistant. In addition, fuels containing high flame speed fuels, such as hydrogen, are known to have severe problems concerning flashback. Flashback can significantly damage injectors, swirlers, and nozzles. The operability of the combustor may be compromised and may cause unscheduled shutdown. On-field gas turbines are typically not well equipped to detect the onset of flashback. The nozzles may have features to control the damage due to flashback, but there is no proven reliable method to detect impending flashback.
It would therefore be desirable to provide a method for detecting an impending flashback or flame holding event in gas turbine engines using combustion dynamics.